1. Field of the Invention
The present invention relates to a power supply system for an electronic instrument. More particularly, the present invention relates to a power supply system for an electronic instrument, capable of avoiding loading of the electronic instrument with a wrong one of plural power source units.
2. Description Related to the Prior Art
A portable type of a television camera with a video tape recorder (hereinafter referred to as video camera) is loaded with a battery pack, a power source adapter, or another power source unit, and is supplied with power by the power source unit. Examples of the battery pack include a type incorporating a storage battery (secondary cell) having been charged by a charger, and a type containing a dry battery (primary cell).
If the battery pack containing a dry battery is loaded on a charger and the charger is operated for charging, there is possibility that gas is generated by the liquid in the dry battery, to raise an inner pressure of the battery to the point of explosion. If the dry battery is a lithium type, spontaneous combustion may occur. If the power source adapter is loaded on to the charger and the charger is operated for charging, the inner circuit of the charger may be damaged.
To avoid the incorrect loading, JP-B 5-12819 and JP-B 5-12820 disclose a construction in which mated fittable faces are provided with a recess and a projection of plural kinds for connection. In a suitable combination, a recess and a projection are fitted on one another, to allow the loading. In an unsuitable combination, a recess and a projection are not engageable, so that improper loading is avoided.
JP-A 4-284349 discloses a video camera in which a cover member is movable between a position for covering power source terminals and a position for uncovering the terminals. While no battery pack is loaded on the video camera, the power source terminals are covered by the cover member, and are protected from deformation, corrosion or other damage. When a battery pack is mounted, an opener member of the battery pack moves the cover member toward the uncovering position in the direction for the loading. This movement of the cover member causes the terminals to emerge. Connecting terminals of the battery pack are connected to the power source terminals, and supplied with power.
However JP-B 5-12819 and JP-B 5-12820 only disclose prevention of improper loading, and not prevention of power source terminals of an electronic instrument from deformation, corrosion or other damages. In JP-A 4-284349, the cover member is only movable. If inadvertently pushed, the cover member is moved to the uncovering position. It is impossible for this cover member reliably to avoid deformation, corrosion or other damage of the terminals, as the cover member is easily moved manually. JP-A 4-284349 does not suggest prevention of improper loading. It would be conceivable to combine those known techniques for the purposes of avoidance of deformation, corrosion or other damage of terminals, and prevention of improper loading. However it would be inevitable that an electronic instrument would have a large space for a relevant mechanism. The electronic instrument could not have the relevant mechanism without being still more voluminous.
In a battery pack of JP-Y 4-526, there is a cover member that is movable between a position for covering power source terminals and a position for uncovering the terminals. In this battery pack, a considerable space is required for containing the cover member. If the volume of the battery pack is kept unchanged, a space for a storage battery must be reduced. When a size of the storage battery is reduced, it is inevitable that the storage battery has small capacity. On the other hand, if the capacity of a storage battery is desired to be greater, the volume of the battery pack should be raised. Accordingly the battery pack disclosed therein cannot be designed compactly. Although a nickel-hydrogen storage battery, with capacity 1.8 times as great as a Ni--Cd battery, could be used in such a battery pack, the battery pack with the movable cover member cannot have greater capacity and a more compact size at the same time.